The present invention relates to apparatus adapted to provide an indication of an angular position of an input member over multiple turns.
Position-indicating devices, such as encoders, are used in many applications, including detecting the position of mechanically-driven actuators required for operating fluid valves, for example. An absolute encoder is an encoder that can identify a position of an input member in an absolute sense, e.g. as a specific angular position. Such encoders may be depowered and will still normally be capable of indicating the position in absolute terms when power is restored, even if the encoder moved whilst the power was off. A multi-turn absolute encoder typically includes several gears in order to determine the absolute position over multiple turns. However, if a sensing device of the encoder happens to fall into an intermediate position, e.g. between two index positions, then the measurement may be indeterminate. Further, if one of the sensing elements fails then the entire encoder device will usually fail.